Originally Posted by Duragrouch

There may be some issues with this. The boss/stud for the caliper take load in tension holding the caliper in place, but also bending in the direction of rotor rotation and pads resisting that motion. A stack of washers will not have the same rigidity if there is any sliding between the washers or spacers and the (original) caliper mounting boss/stud. Even if no sliding, it could also move elastically due to the higher load, small enough you won't see it but enough to cause fatigue failure over time. The total shear load on the bolts would be the same, but since spaced further out, would result in greater bending load on the bolts, with maximum moment in the threaded area. Depending on the height of spacers or washers, bending moment could increase by a multiple. Damage might also happen at the female threaded boss/stud, if not designed for the greater lateral bending load. Check, perhaps due some basic calculations on how much the bending moment is increasing for a given lateral force at the pads. This calculation would not be based on the increase in rotor diameter, but increase in caliper bolt attachment length, specifically, the length between the threaded attachment boss and the underside of the bolt head. If that's increasing by 100% (doubling) or more, or even 50%, caution. You are threading into aluminum, which is notoriously sensitive to loading for fatigue life/failure. Longer bolts is not the same loading condition as longer bosses with same length bolts.